1. Field of the Invention
The invention relates to a lay-flat and removal device for a plastic tube film web produced by means of a film blowing head arranged in a stationary manner, whose lay-flat plates and squeezing rolls may be rotated in a reversing manner around the axis of the supplied film tube, and having a subsequent fixed winding device or device for further processing as well as at least two reversing pneumatic reversal rods and at least two reversing deflection rolls.
2. Description of the Related Art
In the production of tube webs made of plastic film with the aid of blowing processes, tolerances in film thickness cannot be prevented. These tolerances arise, for example, from production tolerances of the blowing head and of the extruder as well as fluctuations of temperature and temperature gradients outside of the extruder. Because the extruded tubes are first laid flat and then wound for further processing, unavoidable thickness tolerances along the circumference of the blown film tube lead to difficulties because the above-mentioned thickness tolerances accumulate in the wound film, form annular rings, and prevent a cylindrical wound film.
The produced film is damaged in this manner and the space-saving storage and further processing of the same is complicated.
In order to prevent the accumulation of thickness tolerances on the wound film, so-called reversing removal devices with pneumatic reversal rods and deflection rolls are used for the tube web. Such devices are known from the literature.
For the purpose of pivoting the reversal elements (pneumatic reversal rods or deflection rolls), EP 0 873 846 recommends, among other things, assigning a rim bearing to each reversal element and providing each reversal element with its own drive motor.
However, such a measure requires large control or even regulation expense so as to control the various drive motors in such a way that the reversal motions of the various pneumatic reversal rods and deflection rolls are precisely coordinated with one another.
Poorly coordinated reversal motions of the pneumatic reversal rods and deflection rolls, which can naturally also be caused by mechanical tolerances in the removal device itself, lead to serious disadvantages such as the formation of creases in the film or an offset of the edges of the film on the rolls. The different mechanical properties of different film materials, of which their friction on the reversal elements and their elasticity are of primary significance in this connection, serve to further complicate the coordination of reversal movements when changing films. Therefore, a device in which each reversal element has its own drive even requires an extensive regulation of reversal movements in order to synchronize the movement of the various reversal elements even when processing different film materials in an appropriate form.
The object of the present invention is therefore to improve a removal device of the type mentioned at the outset in such a way that the expenditure on control and regulation technology is reduced to an economically feasible amount. This object is attained by virtue of the fact that, when at least two pneumatic reversal rods and at least two deflection rolls are used, one pneumatic reversal rod and one deflection roll each form a functional pair. In each functional pair, the deflection roll and the pneumatic reversal rod are mechanically connected to one another in a fixed transmission ratio. The rotational momentum necessary for pivoting the reversal elements of each functional pair is supplied by one motor each.
The mechanical restricted guidance of one deflection roll each and one adjacent pneumatic reversal rod each relative to one another as well as the assignment of one motor each to these two reversal elements of one functional pair structures the regulation in a significantly simpler fashion. In this connection, it is particularly advantageous for the coupling of the movement of the two reversal elements of a functional pair to be in a ratio of 1:2, with other coupling ratios being known as well.
Devices according to the invention have two or more functional pairs. Thus, the possibility exists of varying pivoting motions of the various pairs relative to one another. Thus, for example, the reduction in the pivot angle of various functional pairs that generally occurs in the processing direction can be reduced in order to reverse particularly delicate films more gently.
In the case of the recommended device, processes of this type can optionally be performed by individually controlling the motors assigned to the various functional pairs.
In the case of a plurality of pairs, a steadily slight reduction of the angle of reversal can be provided in the processing direction of the film.